The field of the invention is hard facing of tools and the invention relates more particularly to the hard facing of ground engaging tools to increase the life of such tools. Such tools include harrow discs, plow discs, plow shares, trencher teeth and the like. Various alloy compositions are set forth in the following patents: U.S. Pat. Nos. 3,029,165; 3,603,763; 4,741,974; 5,294,462; 5,332,628; and 5,695,825. The compositions in these patents generally have a very low amount of carbon. The compositions, when applied to ground engaging tools, requires not only wear resistance and hardness, but also a very high degree of bond strength.
Prior art alloys have lacked sufficient bond strength. Many tubular composite metal cored wires have been evaluated for hard facing of agricultural ground engaging tools with the twin arc spray process and the results have been disappointing, particularly relating to poor bonding. The poor bonding between the hard facing deposit and the ground engaging tool has been the leading cause of premature failures. To the date of the present invention, it is believed that no composition can be used without failures in the coating of ground engaging tools.
Various practices are used to place a hard facing on a ground engaging tool. These processes include the oxy-acetylene gas process. Ground engaging tools are preheated to 300-900.degree. F., then the hard facing rod or wire is manually, semi-automatically or automatically melted by oxy-acetylene torch and deposited on the ground engaging tool.
Another process that has been used is the process sold under the trademark DURA FACE. Surface oxides are removed from the ground engaging tool and a hard facing paste or slurry is applied to the surface. The surface is permitted to dry or set and then the coated ground engaging tool is placed in a controlled atmosphere oven and the coating is sintered on the surface.
Another process is the spray fuse process. In this process ground engaging tools are heated to 700-1,000.degree. F. Hard facing powders are sprayed on the heated ground engaging tool through a powder torch. Then the hard facing powder is fused on the ground engaging tool by the powder torch.
The poor bonding between the coating and the ground engaging tool has made such coatings fail to provide a long-lasting coated tool.